User:Sandesf/Nanocluster

Introduction
Nanoclusters are atomically precise, crystalline materials most often existing on the 0-2 nanometer scale. They are often considered kinetically stable intermediates that form during the synthesis of comparatively larger materials such as semiconductor and metallic nanocrystals. The majority of research conducted to study nanoclusters has focused on understanding their mechanistic role in the nucleation and growth mechanisms of larger materials. These nanoclusters can be composed either of a single or of multiple elements, and exhibit attractive electronic, optical, and chemical properties compared to their larger counterparts.

The previously accepted model for nucleation and growth of binary nanomaterials described a metal precursor and either a chalcogen or pnictogen precursor combining to form a singular species that could be described as monomeric. Due to small fluctuations in concentration, these monomers combine together to nucleate crystals followed by further growth through extended monomer combination. This model has now been extended to include the nucleation of cluster species that are generally regarded as a kinetic stable intermediate towards forming nanocrystals. In the midst of nucleation and growth, small crystalline species form that are persistent due to kinetic stability. Clusters have empirically been shown to be favored under conditions of very high monomer concentration.

Clusters themselves lack the applicability of their larger counterparts: nanocrystals. But they can still be used a tool to construct complex nanomaterials thereby extending their applications. There are three main mechanisms that clusters undergo to form nanomaterials: dissolution to renucleation, quantized growth, and aggregation. In the dissolution to renucleation mechanism, the clusters form due to their kinetic stability but over time they are thermally destabilized and eventually decompose into their constituent molecular species. These species then recombine again to directly nucleate nanocrystals thereby bypassing the formation of clusters. In the quantized growth pathway, there must exist cluster species of multiple sizes that are kinetically stable. Upon nucleation to form one cluster species, monomer is quickly added to the surface to form a second, larger but still stable cluster. This process repeats until the larger size of the material no longer dictates atomic precision and more random addition of monomer to the cluster surface results in a nanocrystal. The final process is aggregation in which smaller clusters directly fuse together through oriented attachment that is directed by surface dipoles from unbound surface states.

The importance of Copper Nanoclusters
Copper nanoclusters (CuNCs) are attractive alternatives to other metal nanoclusters. CuNCs is highly efficient, fast, low-cost and does not require any complex operations. Due to its tunable fluorescence and low toxicity, CuNCs has been highly developed for biochemical sensing.

Synthesis and fluorescence properties of copper nanoclusters
CuNCs are easily oxidized and difficult to prepare. However, many approaches are developed to solve this problem. According to the synthesis process, these methods can be mainly classified into several categories, including template-assisted methods, electrochemical synthesis, and etching methods.

Copper nanoclusters synthesized using proteins/peptides as the template
Template syntheses are one of the most common chemical approaches towards CuNCs. Proteins offer several functional chemical groups, such as amine- and carboxyl-groups, which have strong ability to coordinate Cu(II) ions and fix subsequently formed Cu(0) atoms on the protein backbone. Moreover, some proteins also possess reducing ability due to the presence of thiol groups, and thus can work as both template and reductant for CuNCs

Copper nanoclusters synthesized using DNA as the template
DNA is also an interesting ligand for synthesizing different nanomaterials because of its excellent characteristics, including nanosized structure and rich functional groups.

Copper nanoclusters synthesized using polymers as the template
Appropriate functional groups on the polymer backbone can provide multiple binding sites for Cu(II) ions. Using dendrimer as synthetic template and cluster stabilizer, Crooks’ group developed a new method for preparing stable CuNCs composed of a well-defined number of atoms. The cluster size can be controlled by varying the size of the host-dendrimer nanoreactor

Maybe we can just upload this part below into Synthesis and stabilization part as our work？

Copper nanoclusters synthesized using small molecules as the template
Some small molecules are also used as stabilizers or reductants for the synthesis of CuNCs. These small molecules are usually thiols or carboxyl groups, which exhibit good reducibility for metal salts and affinity for metal ions. There is a method for rapid synthesis of GSH-protected CuNCs by ultrasonic treatment. GSH was mixed with Cu(II) ions in an aqueous solution, and the pH was adjusted to 6.0 using NaOH, followed by ultrasonic treatment for 15 minutes. The red-emitting fluorescent CuNCs were obtained after purification. Structural and optical analysis showed that the high density enhanced the co-affinity Cu(I)···Cu(I) interaction between and within NCs, and inhibited the intramolecular vibration and rotation of the ligand. The self-assembly strategy also allows the regularity of CuNCs in the component to be adjusted, resulting in polymorphic CuNCs components with various emission colors.